In recent years, in order to reduce carbon dioxide emitted from cars for prevention of global warming, an electric car or a hybrid car which runs with electric energy instead of or in addition to fuel has attracted attention. In addition, a plug-in-hybrid car configured to allow charging of a battery mounted also in the hybrid car with electric energy from outside of the vehicle has also emerged.
Connection of a charging cable in externally supplying electric power to a car, however, imposes extra burden on a user. Therefore, a non-contact electric power supply system which can start charging without requiring an effort to connect a cable when a car has been parked at a prescribed position has also been studied.
Japanese Patent Laying-Open No. 2010-119246 (PTD 1) discloses a non-contact charging system in which variation in efficiency is detected by transmitting weak electric power while a frequency is varied and a position of a coil is adjusted in accordance with a result of detection.
In addition, Japanese Patent Laying-Open No. 2010-172185 (PTD 2) discloses an electric power reception guidance device capable of notifying a user of an optimal position for charging of a vehicle by informing the user of electric power reception efficiency at a current vehicle position.